Historical Painting Techniques, Materials, and Studio Practice

later transferred to an artificial support at the west end of the hapel) mirrored
the iconography of the Romanesque painting beneath with a few minor
adjustments. The Magdalene in the Deposition was replaced by a centurion
holding a scroll, and the Harrowing of Hell was moved to the recess of the
adjacent south wall and paired with the Noli me Tangere. Above this recess is
the Entry into Jerusalem and a newly identified scene of the Washing of Christ's
Feet (3). Within the western recess of the south wall are scenes of the Martyrdom
of St. Catherine of Alexandria. A striking image of Christ as Pantocreator,
surrounded by evangelist symbols, fills the eastern segment of the vault,
while the remaining segments are painted with Infancy scenes (Annunciation,
Nativity, and Annunciation to the Shepherds) , foliage, and busts in roundels.
Other thirteenth-century painting survives on the northern arches of the
chapel.
Conservation history
Until the conservation program in the 1960s, very little of the twelfth-century
painting was visible, as it lay beneath the later scheme. The thirteenth-century
painting was itself in extremely poor condition, due to the combination of
humidity and the wax coating and hair nets applied by Professor Tristram in
the 1920s to consolidate the surface (4) . The conservation campaign in the
1960s involved the following: transfer of the thirteenth-century painting on
the east wall to an artificial support at the west end; detachment and replacement
in situ of other areas of thirteenth-century painting; transfer of the
mitered head and sinopia from the twelfth-century scheme onto the north
wall; partial removal of the wax coating; and consolidation with skimmed
milk and lime water. This complex conservation history has far-reaching implications
for the conclusions that can be drawn for the original technique
of the thirteenth-century paintings.
Technique of the twelfth-century painting
Plaster. Information on the construction mortar, depth, and stratigraphy of
the Romanesque plaster is largely concealed by edging repairs and fills. There
are, however, two areas which supply valuable evidence for the original technique.
The ashlar support is visible at dado level where the plaster has been
lost, and it is clear that a single plaster layer approximately 0.5 cm in thickness
was applied to the stone. Elsewhere there are two distinct plaster layers: the
uppermost layer, the intonaco, is approximately 0.5 cm in thickness, while
below that a slightly coarser and more yellow plaster appears to be about 1.0
cm thick. It seems reasonable to assume that a layer of plaster was applied to
level the masonry where necessary, and that the intonaco was then either
applied over this, or directly on to the stone.
Unfortunately, it was not possible to take a sufficiently large sample for full
analysis of the original plaster, but from visual examination of the polished
cross sections it was estimated that a fmely graded inert aggregate, principally
subangular quartz, was combined with lime in a ratio of approximately 2: 1
to create the intonaco. The conspicuous addition of chopped straw and fibers
to the plaster suggests that they were included to increase the mechanical
strength of the render. This organic material may have had the additional
function of acting as a mechanical buffer by absorbing moisture during the
setting of the plaster (5). In some samples, it is also clear that charcoal particles
have been incorporated, with the greatest concentration beneath areas that
are predominantly blue (Plate 20, samples 3 and 5). It seems likely that the
charcoal was incorporated to reduce the light scatter from the white substrate,
thereby increasing the covering power of the blue mineral pigments.
Although the surface texture itself is fairly smooth, the overall topography of
the painted surface is remarkably uneven . The application of the plaster is
rather crude, with deep undulations readily visible in raking light (6) .
There are two principal horizontal zones of plaster corresponding to the
narrative registers, and another for the ornamental border that divides these
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